Elliptically polarizing plate and organic light-emitting diode

An elliptically polarizing plate comprising, sequentially, a linear polarizer, a first retardation film, a second retardation film, a third retardation film and a fourth retardation film,

• wherein the first retardation film is a −B plate having an Nz value of more than 1 in Equation 1:
• Nz=(nx−nz)/(nx−ny), [Equation 1]
• wherein the second retardation film is a +B plate having an Nz value of less than 0 in Equation 1, or a +C plate satisfying Expression 1:
• nx=ny<nz, [Expression 1]
• wherein the third retardation film has an Nz value of 0.8 to 1.2 in Equation 1, and wherein an in-plane slow axis of the third retardation film forms an angle of 43 degrees to 47 degrees with an absorption axis of the linear polarizer,
• wherein the fourth retardation film is a +B plate having a Nz value of −4.0 or less in Equation 1, or a +C plate satisfying Expression 1, and
• wherein a sum of a thickness direction retardation value of the first retardation film and a thickness direction retardation value of the second retardation film is in a range of −100 nm to 130 nm and a thickness direction retardation value (Rth) is calculated according to Equation 2:
• Rth=(nz−ny)×d, [Equation 2]
• wherein, nx, ny and nz are refractive indexes of the first to fourth retardation films in x-axis, y-axis and z-axis directions, respectively, and
• wherein the x-axis is a direction parallel to an in-plane slow axis of the first to fourth retardation films, the y-axis is a direction parallel to an in-plane fast axis of each of the first to fourth retardation films, the z-axis is a thickness direction of the first to fourth retardation films, and d is a thickness of the first to fourth retardation films.